1. Field of Invention
The invention relates to a mixed metal oxide catalytic system for the selective oxidation of propylene to acrylic acid and acrolein. The novel catalytic system contains molybdenum, vanadium, palladium, lanthanum, niobium, and X, where X is copper, chromium or mixtures thereof. The novel catalytic system provides higher yields of acrylic acid and acrolein in the low temperature oxidation of propylene with molecular oxygen-containing gas without the production of side products such as CO. The invention also relates to methods of making and using the catalytic systems.
2. Description of Related Art
Several publications are referenced in this application. These references describe the state of the art to which this invention pertains, and are hereby incorporated by reference.
The catalytic vapor phase oxidation of propylene for the production of acrylic acid in two stages is known in the art. The first stage reaction converts propylene to mainly acrolein. The second stage converts acrolein to mainly acrylic acid. Attempts of improving the process conditions in the first stage have focused on the following drawbacks:
i. Increases in the propylene content in the feed gas being limited because of the heat of reaction. Particularly, when the reaction is carried out at higher temperatures. PA1 ii. The reaction system must be protected from the danger of explosion at higher reaction temperatures. PA1 iii. The selectivity to useful oxidation products is not enhanced when the reaction is carried out at higher temperatures because some of the propylene feed converts through total oxidation to products such as carbon dioxide and water. PA1 wherein: X=Cu or Cr or both; PA1 a is 1; PA1 b is 0.01 to 0.9; PA1 c is &gt;0 to 0.2, preferably 0.0000001 to 0.2; PA1 d is 0.0000001 to 0.2; PA1 e is 0 to 0.2, preferably 0.0000001 to 0.2; and PA1 f is 0 to 0.2, preferably 0.0000001 to 0.2.
Under these circumstances, various studies have been directed to improving the reaction conditions of these processes. U.S. Pat. No. 5,218,146 relates to a process for the production of acrylic acid by a two stage catalytic vapor phase oxidation of propylene with molecular oxygen. The first stage involves the oxidation of propylene to mainly acrolein, which comprises supplying to the first stage of the reaction a mixture containing propylene, molecular oxygen, propane, carbon dioxide, carbon monoxide and steam and using a MoFeB mixed metal oxide catalyst. The reaction temperature is in the range of 250 to 450.degree. C., the preferred range is 320-335.degree. C. .fwdarw.T 40-60.degree. C. was observed in the reactor. Thus the highest temperature observed in the reactor may go up to as high as 400.degree. C. This reaction temperature is quite high for any oxidation reaction requiring close control of operational parameters, particularly close control of the concentration of oxygen and propylene.
European Patent 0 630 879 A1 relates to a process for producing an unsaturated aldehyde and an unsaturated acid which comprises subjecting propylene to gas phase catalytic oxidation with molecular oxygen in the presence of a catalyst comprising a composite oxide of the formula Mo.sub.a Bi.sub.b Fe.sub.c A.sub.d B.sub.e C.sub.f D.sub.g O.sub.x at 310.degree. C., wherein: A represents nickel and/or cobalt; B represents at least one element selected from phosphorus, boron, arsenic, tellurium, tungsten, antimony and silicon; and D represents at least one element selected from potassium, rubidium, cesium and thallium; and wherein a, b, c, d, e, f, g and x represent, respectively, the number of atoms of Mo, Bi, Fe, A, B, C, D and O, and where a is 12, 0&lt;b.ltoreq.10, 0&lt;c.ltoreq.10, 1.ltoreq.d.ltoreq.10, 0.ltoreq.e.ltoreq.10, 0.ltoreq.f.ltoreq.10 and 0&lt;g.ltoreq.2 and x has a value dependent on the oxidation state of the respective elements. At a conversion of 80.5%, a selectively of 90.2% for acrolein and acrylic acid was reported.
European Patent 0 293 224 A1 relates to a process for the production of acrolein from propylene using the catalyst Mo.sub.a W.sub.b Bi.sub.c Fe.sub.d A.sub.e B.sub.f C.sub.g D.sub.h O.sub.x, wherein A is an element selected from the group consisting of nickel and cobalt; B is at least one element selected from the group consisting of alkali metals, alkaline earth metals and thallium; C is at least one element selected from the group consisting of phosphorus, arsenic, boron and niobium; and D is at least one element selected from the group consisting of silicon, aluminum and titanium and the subscripts a, b, c, d, e, f, g, h and x are respectively the number of atoms of the elements Mo, W, Bi, Fe, A, B, C, D and O, provided that a=2 to 10, b=0 to 10, on condition that a+b=12, c=0.1 to 10, d=0.1 to 10, e=2 to 20, f=0.005 to 3.0, g=0 to 4, h=0.5 to 15 and x is a number required to satisfy the valence requirements of the other elements. The reaction temperature was 330.degree. C.
Another European Patent 0 145 467 A3 relates to the catalytic oxidation of olefins to .alpha., B unsaturated carboxylic acids and aldehydes at a temperature in the range 65-80.degree. C., but carried out at a high pressure in the range 71 to 168 psi. Moreover, the method was operated in liquid phase in batch mode. At the end of 4 hours, a 31.0 g/l catalyst yield of acrylic acid was obtained. This system has several disadvantages such as requiring a batch mode operation, a high pressure liquid phase reaction, catalyst recovery, activation, etc.
None of the prior art has disclosed or suggested the advantages of the catalysts disclosed in present invention which provide high performance for selective production of acrylic acid and acrolein through a gas phase partial oxidation process of propylene with zero or insignificant production of carbon monoxide at low temperatures.
Accordingly, it would be desirable to produce an improved catalyst for use in the selective production of acrylic acid and acrolein without the production of carbon monoxide.